Use the Following to Answer the Following Questions -Tubulin Is a Dimer, Made Up of 2 Slightly Different

Multiple Choice

Use the following to answer the following questions. All three are involved in maintenance of cell shape.
$\begin{array}{c}\begin{array}{|l}\hline\\ \text {Property}\\\hline\\\\ \text {Structure}\\\hline\\ \text {Diameter}\\\hline \text {Main}\\\text {functions}\\\hline \end{array}\begin{array}{|l|}\hline \text { Microtubules (tubulin}\\\text { polymers) }\\\hline \text {Hollow tubes; wall}\\ \text {consists of 13 columns}\\ \text {of tubulin molecules}\\\hline \text {\( 25 \mathrm{~nm} \) with 15-nm}\\ \text {lumen}\\\hline\\ \text {Cell motility}\\\hline \end{array}\begin{array}{l|}\hline \text { Microfilaments (actin}\\ \text { filaments) }\\\hline \text { Two intertwined strands}\\ \text { of actin, each a polymer }\\ \text { of actin subunits}\\\hline\\ \text { \( 7 \mathrm{~nm} \) }\\\hline\\ \text { Cell motility}\\\hline \end{array}\begin{array}{l|}\hline \text {Intermediate}\\ \text {filaments}\\\hline \text {Fibrous proteins }\\ \text {supercoiled into}\\ \text { thicker cables}\\\hline\\ \text {8-12nm}\\\hline\\ \text {Anchorage}\\\hline\end{array}\end{array}$

-Tubulin is a dimer, made up of 2 slightly different polypeptides, alpha and beta. Given the structure above, what is the most likely consequence to the structure of the microtubule?

A) One "half-pipe" side of the tubule must be heavier in alpha and the other in beta subunits.
B) One end of a microtubule can grow or release dimers at a faster rate than the other.
C) Microtubules grow by adding a complete circular layer at a time rather than spiraling.
D) Microtubules in cilia must never grow or become shorter.
E) Tubulin molecules themselves must be rigid structures.